Welcome to greater London: 7 million people, 600 square miles and enough underground tubes to get lost within. We left it earlier this week, so enjoy what I learned.

Like we’ll tell you again and again - and practice ourselves - get underground in each and every city you visit. In the states, abroad, wherever, use a city’s mass transit because no evaluation of a city is complete without a ride on its buses, trains, or whatever else. Know how its people transit, and see its priorities.

London, like a handful of other international cities - Tokyo, Paris, Los Angeles and New York (my own Philadelphia lags out a bit in this category) - claims the world’s finest mass transit system.

Here you’ll pay by zones, so, of course your payment methods should be dictated by your patterns. Major stations have friendly-enough attendants from whom you can purchase one and three day passes. If you’re looking to use the transit over a longer period of time, grab an Oyster card. For a 3 pound deposit - remember to turn the card back in before you leave - and however much you want to put on the card, you can swipe onto any train - tube, overground or otherwise - or bus. Take it out of that obnoxious plastic case it comes in and put it into your wallet - swipe it through the wallet and look like you know what you’re doing. Remember to always swipe before you get onto the train and after you get off - buses just when getting on.

At 90 pence per ride as of writing, those might just be the only thing I would call cheap in this city - admittedly after just a short crash. Get on at least one of those signature red double decker buses; ride on top to be sure and in the front if you can.

Anyone have their own London tube experiences?

We’ll be sure to compare London’s system with others as our travels continue.